The overall goal of our studies is to understand the regulation, function, and disease association of the keratin intermediate filament (IF) proteins, keratin polypeptides 8, 18 and 19 (K8, K18 and K19). These keratins are the major IF proteins in epithelia of digestive organs. The functions of the epithelial-specific keratins remain poorly understood but their relevance to human disease is well established. For example, several skin diseases are caused by mutations in epidermal keratins, and more recently K8 and K18 mutations were identified in patients with cirrhosis. Our overall hypothesis is that IF proteins, one of the three major cytoskeletal protein families that include actin microfilaments and tubulin microtubules, play important physiologic and disease-related roles whose significance is rapidly unfolding. Our specific aims are: (i) Study the significance of the liver disease-associated K8 Arg340-to-His mutation. The Arg340-to-His mutation is the most common keratin mutation identified to date in patients with cirrhosis. This aim is based on the hypothesis that mutation of this highly conserved arginine alters keratin function and thereby predisposes simple-type epithelial cells to injury. (ii) Study the significance of K8 Serine-73 phosphorylation in digestive organs. (iii) Use a reverse immunologic approach to characterize K8, K18 and K19 regulation via phosphorylation. The hypothesis for Aims 2 and 3 is that keratin phosphorylation plays important roles, positively or negatively, in modulating cytoprotection and other cellular functions. (iv) Study the biologic significance of K19 and K18 fragmentation during apoptosis in cells and tissues. This aim is based on the hypothesis that keratin degradation is important for epithelial cell apoptosis, and that interfering with such degradation during apoptosis may have a significant impact on cell turn-over in digestive organs. Our proposed studies are likely to generate important new biologic information regarding keratins in the digestive system, and to help clarify their function and role in human disease. [unreadable] [unreadable]